Filter with variable pleat depth

ABSTRACT

A filter is provided by pleated filter media having a plurality of pleats defined by wall segments extending axially along an axial direction along an axis and extending transversely along a transverse direction between first and second sets of pleat tips at first and second sets of axially extending bend lines. The pleated filter media spans laterally along a lateral span along a lateral direction, with the wall segments being spaced from each other by lateral gaps. The pleats have a pleat depth along the transverse direction along the wall segments between the first and second sets of pleat tips. The pleat depth varies as the pleated filter media spans laterally along the lateral direction.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.11/327,613, filed Jan. 6, 2006.

BACKGROUND AND SUMMARY

The invention relates to filters, and more particularly to pleatedfilters.

The invention arose during continuing development efforts directedtoward improvements, including space utilization, in pleated filterelements.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view partially cut away of a filter known in theprior art.

FIG. 2 is a perspective view of a portion of the assembly of FIG. 1.

FIG. 3 is a top elevation view of the pleated filter element of FIG. 2.

FIG. 4 is a view like FIG. 3 and illustrates the present invention.

FIG. 5 is a perspective view of the filter element of FIG. 4.

FIG. 6 is like FIG. 4 and shows another embodiment.

FIG. 7 is like FIG. 4 and shows another embodiment.

FIG. 8 is like FIG. 4 and shows another embodiment.

FIG. 9 is like FIG. 4 and shows another embodiment.

FIG. 10 is like FIG. 4 and shows another embodiment.

FIG. 11 is like FIG. 4 and shows another embodiment.

FIG. 12 is a perspective view of the filter element of FIG. 11.

FIG. 13 is like FIG. 11 and shows another embodiment.

FIG. 14 is like FIG. 4 and shows another embodiment.

FIG. 15 is a perspective view of the filter element of FIG. 14.

FIG. 16 is like FIG. 14 and shows a further embodiment.

FIG. 17 is a perspective view of the assembly of FIG. 16.

DETAILED DESCRIPTION

FIG. 1 shows a filter 20 like that shown in U.S. Pat. No. 6,478,959,incorporated herein by reference. The filter filters fluid flowing alonga flow path 22 having first and second segments, the first segment 24being a filtering path segment, and the second segment 26 being an axialflow path segment extending axially along an axial direction along axis28. First segment 24 is normal to second segment 26. The filter isprovided by a filter media sheet 30, FIG. 2, providing an annularpleated filter element 32 extending axially along the noted axialdirection, and having a plurality of inner pleat tips 34, FIGS. 2, 3,defining a hollow filter interior 36, and having a plurality of outerpleat tips 38. The filter may have inner and outer liners 40 and 42 atrespective inner and outer pleat tips 34 and 38, and may have sealingend caps 44 and 46 at the axial ends of the pleats, all as is known.Fluid to be filtered may flow radially inwardly as shown at 24 throughthe filter element, thus providing an outside-in filter. Alternatively,the fluid may flow in the opposite direction, namely radially outwardlythrough the filter element, thus providing an inside-out filter, all asis known.

In other embodiments known in the prior art, the pleats are alternatelysealed to each other at their upstream and downstream axial ends toprovide a direct flow filter, for example as shown in U.S. Pat. Nos.6,375,700, 6,482,247, 6,511,599, incorporated herein by reference. Fluidto be filtered flows along an axial flow path through the filterelement. The alternate sealing of the upstream and downstream ends ofthe channels between the pleats provides a first set of flow channelsopen at their upstream ends and closed at their downstream ends, and asecond set of flow channels closed at their upstream ends and open attheir downstream ends, all as is known. In such embodiments, fluid flowsaxially upwardly or downwardly in FIGS. 1, 2, and ends caps 44, 46 andliners 40, 42 are omitted.

FIGS. 4, 5 show a filter 50 including pleated filter media 52 having aplurality of pleats 54 defined by wall segments 56 extending axiallyalong an axial direction along axis 28 and extending transversely alonga transverse direction 58 between first and second sets of pleat tips 60and 62 at first and second sets of axially extending bend lines 64 and66, respectively. Transverse direction 58 is normal to axial direction28. Pleated filter media 52 spans laterally along a lateral span along alateral direction 68. Wall segments 56 are spaced from each other bylateral gaps 70 along lateral direction 68. Lateral direction 68 isnormal to transverse direction 58 and normal to axial direction 28.Pleats 54 have a pleat depth 72 along transverse direction 58 along wallsegments 56 between the first and second sets of pleat tips 60 and 62.Pleat depth 72 varies as pleated filter media 52 spans laterally alonglateral direction 68, for example as shown at pleat depth 72 a thenshorter pleat depth 72 b then shortest pleat depth 72 c.

A first wall segment such as 56 a, FIG. 4, has a first pleat depth suchas 72 a, and a second wall segment such as 56 b has a second pleat depthsuch as 72 b different than first pleat depth 72 a, and a third wallsegment such as 56 c has a third pleat depth such as 72 c different thanthe first and second pleat depths 72 a and 72 b, and so on. Thedifferent depth wall segments may be laterally adjacent each other andbe separated by a single lateral gap therebetween, for example as theclosed-loop shape of the filter begins to curve, for example at 74, orthe different depth wall segments may be laterally spaced by a pluralityof other wall segments and lateral gaps therebetween, for examplecomparing the wall segment depth along a straight-run of the filter asat 76 vs. the wall segment pleat depth at a curve or turn such as 78.Pleated filter media 52 spans along an annulus 80 in a plane normal toaxis 28. As used herein, an annulus or annular shape includes theracetrack shape as shown and any other closed-loop shape includingcircular shapes, oval shapes, obround shapes, eccentric shapes, and soon. In FIGS. 4, 5, the annular shape has a first span section such as 78and a second span section such as 76, wherein the first span section iscurved and has a pleat depth less than the pleat depth at second spansection 76.

In FIGS. 4, 5 annular shape 80 defines a hollow interior 82 elongatedalong a longitudinal direction 84 in the noted plane normal to axis 28.Annular shape 80 has two distally oppositely longitudinally spacedcurved span sections 78 and 86 joined by a pair of longitudinal sections76 and 88 extending longitudinally therebetween. The pleat depth at thetwo curved span sections 78, 86, e.g. pleat depth 72 c, is less than thepleat depth at the pair of longitudinal sections 76, 88, e.g. pleatdepth 72 a.

FIG. 6 shows another embodiment and uses like reference numerals fromabove where appropriate to facilitate understanding. In FIG. 6, pleatdepth 72 d at one or both curved span sections 88, 90 is less than pleatdepth 72 e at longitudinal section 92, and may or may not be less thanpleat depth 72 f at longitudinal section 94. In one embodiment, pleatdepth 72 e at longitudinal section 92 is greater than pleat depth 72 fat longitudinal section 94, as shown. Annular shape 96 in FIG. 6 has anouter perimeter 98 having a longitudinally extending first longitudinalcenterline 100 in the noted plane normal to axis 28, i.e. the plane ofthe page in FIG. 6. Annular shape 96 has an inner perimeter 102 having alongitudinally extending second longitudinal centerline 104 in the notedplane normal to axis 28. Inner perimeter 102 defines hollow interior 106of the filter element. First and second longitudinal centerlines 100 and104 are transversely offset from each other along transverse direction58.

FIG. 7 shows another embodiment and uses like reference numerals fromabove where appropriate to facilitate understanding. In the annularshape 107 in FIG. 7, the pleat depth of at least one of and preferablyboth of longitudinal sections 108 and 110 varies as the respectivelongitudinal section spans laterally along lateral direction 68 andlongitudinally along the noted longitudinal direction 84, for example asshown at pleat depth 72 g greater than pleat depth 72 h. Longitudinalsection 108 has a first pleat depth 72 h adjacent curved span section112, a second pleat depth 72 g intermediate the two curved span sections112 and 114, and a third pleat depth 72 i adjacent the other curved spansection 114. Second pleat depth 72 g is different than the first andthird pleat depths 72 h and 72 i. In FIG. 7, second pleat depth 72 g isgreater than first and third pleat depths 72 h and 72 i. Longitudinalsection 110 is comparable. Hollow interior 116 of the filter element ofFIG. 7 has a barbell shape in the noted plane normal to axis 28, i.e. inthe plane of the page of FIG. 7. The barbell shape has a pair oflongitudinally distally oppositely spaced transverse width sections 118and 120 at the two curved span sections 112 and 114, respectively, andhas an intermediate narrower transverse width section 122 extendinglongitudinally therebetween.

FIG. 8 shows another embodiment and uses like reference numerals fromabove where appropriate to facilitate understanding. The annular shape123 in FIG. 8 has a pair of longitudinal sections 124 and 126 extendinglongitudinally between curved span sections 128 and 130. The pleat depthof longitudinal section 126 varies as such longitudinal section spanslaterally along lateral direction 68 and longitudinally alonglongitudinal direction 84. Longitudinal section 126 has a first pleatdepth 72 j adjacent curved span section 128, a second pleat depth 72 kintermediate the two curved span sections 128 and 130, and a third pleatdepth 72 m adjacent curved span section 130. Second pleat depth 72 k isless than first and third pleat depths 72 j and 72 m.

FIG. 9 shows another embodiment and uses like reference numerals fromabove where appropriate to facilitate understanding. Annular shape 132in FIG. 9 has an outer perimeter 134 having an axially extending firstaxial centerline 136 extending along axis 28, i.e. into the plane of thepage of FIG. 9 and perpendicular thereto. Annular shape 132 has an innerperimeter 138 defining a hollow interior 140 of the filter element andhaving an axially extending second axial centerline 142 extending alongthe noted axial direction 28. First and second axial centerlines 136 and142 are transversely offset from each other along the noted transversedirection 58. Inner and outer perimeters 138 and 134 are eccentricrelative to each other. In the embodiment of FIG. 9, each of inner andouter perimeters 138 and 134 is circular. Pleat depth 72 n at curvedspan section 144 is less than pleat depth 72 p at curved span section146.

FIG. 10 shows another embodiment and uses like reference numerals fromabove where appropriate to facilitate understanding. The pleated filtermedia has first, second, third, and fourth panels 152, 154, 156 and 158spanning laterally along lateral direction 68 in a plane normal to axis28, i.e. in the plane of the page of FIG. 10, and defining first andsecond hollow interiors 160 and 162. Panel 152 has first, second andthird span sections 164, 166 and 168, with second span section 166 beinglaterally between first and third span sections 164 and 168. The pleatdepth 72 r of second span section 166 is greater than the pleat depths72 q and 72 s of first and third span sections 164 and 168. Fourth panel158 has first, second and third span sections 170, 172 and 174, withsecond span section 172 being laterally between first and third spansections 170 and 174. The pleat depth 72 u of second span section 172 isgreater than the pleat depths 72 t and 72 v of first and third spansections 170 and 174. Hollow interior 160 is elongated alonglongitudinal direction 84 in the noted plane normal to axis 28. Panel152 has two distally oppositely longitudinally spaced span sections 164and 168 joined by intermediate span section 166 extending longitudinallytherebetween. Hollow interior 162 is elongated along longitudinaldirection 84 in the noted plane normal to axis 28. Panel 158 has twodistally oppositely longitudinally spaced span sections 170 and 174joined by intermediate span section 172 extending longitudinallytherebetween. Hollow interior 160 is transversely spaced between panels152 and 154 along the noted transverse direction 58. Hollow interior 162is transversely spaced between panels 156 and 158 along the notedtransverse direction 58. Panels 154 and 156 are transversely adjacenteach other and transversely spaced between hollow interiors 160 and 162and panels 152 and 158. Hollow interior 160 and/or 162 may be enclosedat their longitudinal ends by surrounding filter media or an enclosinghousing such as 176, which may also include a wall 178 between panels154 and 156.

FIGS. 11, 12 show another embodiment and use like reference numeralsfrom above where appropriate to facilitate understanding. Pleated filtermedia 180 spans laterally along lateral direction 68 from a first spansection 182 to a second span section 184 to a third span section 186. Inthis embodiment, the pleated filter media spans rectilinearly alongfirst, second, third span sections 182, 184, 186, without curved orclosing-loop sections as above in FIGS. 4-9. The pleat depth 72 x ofsecond span section 184 is greater than the pleat depths 72 w and 72 yof first and third span sections 182 and 186. In other embodiments,pleat depth 72 x is less than pleat depths 72 w and 72 y. Pleat depths72 w and 72 y may or may not be the same.

FIG. 13 shows another embodiment and uses like reference numerals fromabove where appropriate to facilitate understanding. FIG. 13 showstransition span section 188 between sections 182 and 184, and transitionspan section 190 between sections 184 and 186, of varying transitionpleat depth.

Varying the pleat depth of filter media at strategic locationsthroughout the filter can be useful for increased performance, and toaccommodate various space envelopes. Reducing pleat depth in the radiussections of round, oval or racetrack filters reduces restriction,increases capacity, and allows for increased media area. Conventionalsingle depth pleating often will result in blind-off pleats in theradius sections of such filters, and thus the media in that region isnot fully utilized. Variable pleat depths in panel filters enable uniquedesigns that will fully use the space available. Changing the pleatdepth will allow for media area to be maximized, and filter performanceincreased. Performance is increased because variable pleat depth allowsfor more and/or better utilization of the filter media. By reducing thepleat depth in the radius or curved span sections of filters, the insidepleat tips remain open for fluid flow, rather than blinding-off of suchpleats. In the past, with conventional single depth pleating, to preventblind-off of pleats in radius or curved or corner sections, the pleatheight is reduced throughout the entire filter, to accommodate suchcurved sections without blinding-off same. Variable pleat height alsoenables increased media to be added to the straight sections of filters,as shown. In panel filter designs, FIGS. 11-13, an extended pleat depthsection may be provided in the middle and/or reduced pleat depthsections on the sides, or vice versa. The added media is not possiblewith conventional single depth pleating. The additional media providesincreased performance for panel filters. The variable depth also enablesoffset inlet or outlet designs, e.g. FIGS. 6, 9, for additional media.Conventional pleating would require using the reduced pleat depththroughout the filter, thus resulting in less media area. FIG. 8 showsvariable pleating allowing a filter to be designed around physicalobstructions, e.g. at 131. This type of design may be used on variousfilter shapes, and allows filter designs that are not possible withconventional single depth pleating. As noted above, the designs may beused in direct flow type filters where the pleat ends are alternatelysealed and fluid flows in the noted axial direction 28 along the lengthof the pleat and/or along the depth of the pleat along transversedirection 58 and/or laterally through the pleat wall segment alonglateral direction 68. The present designs enable the space allowed forfilters and housings to be customized and not limited to currentconstraints. The designs further allow for different pleat depthsthroughout the filter as needed for performance and/or structuralreasons. This variable pleating could allow for structural voids withinthe pleated area or other design characteristics such as offset inletsand outlets.

FIGS. 14, 15 show another embodiment and use like reference numeralsfrom above where appropriate to facilitate understanding. Filter element200 includes a pair of panels 202 and 204 mating to form a closed-loopannulus. Panel 202 is a pleated filter media sheet 206 having aplurality of pleats 208 defined by wall segments 210 extending alongtransverse direction 58 between first and second sets of pleat tips 212and 214 at first and second sets of axially extending bend lines 216 and218. Wall segments 210 extend axially between first and second axialends 220 and 222. Panel 202 spans laterally along a lateral span alonglateral direction 68 from a first lateral end 224 to a second lateralend 226. Wall segments 210 have the noted pleat depth 72 alongtransverse direction 58 between the first and second sets of pleat tips212 and 214. The depth of wall segments 210 varies as panel 202 spanslaterally along its lateral span along lateral direction 68 from firstlateral end 224 to second lateral end 226, i.e. left to right in FIG.14, for example as shown at pleat depth 72 aa increasing to pleat depth72 bb then decreasing to pleat depth 72 cc.

Second panel 204 is provided by a second pleated filter media sheet 228having a plurality of pleats 230 defined by wall segments 232 extendingalong the noted transverse direction 58 between third and fourth sets ofpleat tips 234 and 236 at third and fourth sets of axially extendingbend lines 238 and 240. Wall segments 232 of second panel 204 extendaxially between third and fourth axial ends 242 and 244. Second panel204 spans laterally along a lateral span along the noted lateraldirection 68 from a third lateral end 246 to a fourth lateral end 248.Wall segments 232 of panel 204 have pleat depth 72 along the notedtransverse direction 58 between the third and fourth sets of pleat tips234 and 236. The pleat depth of wall segments 232 of panel 204 varies aspanel 204 spans laterally along lateral direction 68 from third lateralend 246 to fourth lateral end 248, as shown at pleat depth 72 ddincreasing to pleat depth 72 ee then decreasing to pleat depth 72 ff.

The pleat depth of wall segments 210 along transverse direction 58 offirst panel 202 varies as panel 202 spans laterally along lateraldirection 68 from first lateral end 224 to second lateral end 226 suchthat wall segments 210 have a minimum pleat depth such as 72 aa at firstlateral end 224, then increase to a maximum pleat depth such as 72 bb ata central region 250 between first and second lateral ends 224 and 226,then decrease to a minimum pleat depth 72 cc at second lateral end 226.The pleat depth of wall segments 232 along transverse direction 58 ofsecond panel 204 varies as panel 204 spans laterally along lateraldirection 68 from third lateral end 246 to fourth lateral end 248 suchthat wall segments 232 of second panel 204 have a minimum pleat depthsuch as 72 dd at third lateral end 246, then increase to a maximum pleatdepth such as 72 ee at a central region 252 between third and fourthlateral ends 246 and 248, then decrease to a minimum pleat depth such as72 ff at fourth lateral end 248.

Minimum pleat depth wall segments 210 at first and second laterals ends224 and 226 of first panel 202 are distally opposite each other along afirst chord, for example as shown in dashed line at 254, extending alongthe noted lateral direction 68 through the annular filter element.Minimum pleat depth wall segments 232 at third and fourth lateral ends246 and 248 of second panel 204 are distally opposite each other along asecond chord, for example as shown at dashed line 256, extending alongthe noted lateral direction 68 through the annular filter element.Chords 254 and 256 are preferably parallel to each other. First chord254 preferably extends parallel to a projection line, for example asshown in dashed line at 258, extending laterally along lateral direction68 through the axial centerline of the annular filter element. Secondchord 256 extends parallel to projection line 258 and on the oppositetransverse side thereof from first chord 254. Chords 254 and 256 arespaced by a transverse gap 260 therebetween. The noted axial flow pathsegment 26 extends axially through gap 260, i.e. out of the page in FIG.14. Minimum pleat depth wall segments 210 at first lateral end 224 offirst panel 202 are diametrically opposite minimum pleat depth wallsegments 232 at fourth lateral end 248 of second panel 204. Minimumpleat depth wall segments 210 at second lateral end 226 of first panel202 are diametrically opposite minimum pleat depth wall segments 232 atthird lateral end 246 of second panel 204. In the preferred embodimentof FIGS. 14, 15, the annular filter element is cylindrical, though otherannular configurations may be used, such as oval shaped, racetrackshaped, obround shaped, and other closed-loop shapes. In preferred form,the first set of pleat tips 212 lie along a first rectilinear projectionline 254 extending along lateral direction 68, and the third set ofpleat tips 234 lie along a second rectilinear projection line 256extending along lateral direction 68 and transversely spaced from firstrectilinear projection line 254. The first and second panels 202 and 204are sealed together along axial sealing strips such as shown in dashedline at 262 and 264. The filter element may have inner and outer linersand sealing axial end caps, as above. The fluid flow direction may beoutside-in, as shown in FIG. 1, or inside-out which is the reverse ofthat shown in FIG. 1. Further alternatively, a direct flow filter may beprovided wherein the fluid flows axially through the filter, wherein thechannels between the pleated wall segments are alternately sealed toeach other at the upstream and downstream axial ends to provide a firstset of flow channels open at their upstream ends and closed at theirdownstream ends, and a second set of flow channels closed at theirupstream ends and open at their downstream ends, as above noted.

A filter of the above noted geometry, including outside-in flow andinside-out flow, may have ends that are sealed by a formed or molded endcap that may communicate flow from the interior of the annular shape toan inlet or outlet. Typically, one end is completely sealed, e.g. thebottom end in FIGS. 1, 17; and the opposite axial end, e.g. the upperend in FIGS. 1, 17, has a shape or seal defined by its mating surface toa filter head or plenum. This may be useful if the filter is housed in acan and needs to attach or seal to a nut plate or filter head. Becausethe geometry lends itself to placing each filter half 202 and 204 in amold or tool, such semi-circular shape or other arcuate portion of aclosed-loop annulus, lends itself to injection molding. Eachsemi-circular or arcuate shaped half may have a formed frame that whenjoined around the perimeter forms a sealed unit. Additionally, these twohalves may be identical or mirror images of each other with details thatallow them to seal or snap together. The axial ends may be closed oropen to communicate flow from the interior of the annular element to aninlet or outlet plenum or mating surface. An advantage of the pleatedconfiguration is the ability to place the pleated section in a moldingtool and form the frame or support around it, which may otherwise bedifficult with radial pleats. Additionally, the two halves may be formedsimultaneously where the middle of the form becomes a hinge, e.g. at thelocation of line 262, and the outer edges seal to become a completeunit. A support grid or structure or liner may be provided within therectangular annulus 260 of the filter to provide resistance todifferential pressure, and stabilize the pleat structure.

FIGS. 16, 17 show a first end cap 266 mounted to first pleated mediasheet 206 of first panel 202 at first axial end 220 of wall segments 210of first pleated filter media sheet 206. A second end cap 268 is mountedto second pleated filter media sheet 228 of second panel 204 at thirdaxial end 242 of wall segments 232 of second pleated filter media sheet228. First and second end caps 266 and 268 are mated and sealed to eachother, e.g. as shown along dashed line 270, and span laterally along thenoted lateral direction 68 and transversely along the noted transversedirection 58. Each end cap is initially mounted and sealed to itsrespective filter media sheet of its respective panel, and then thesesubassemblies are mounted to each other, with end caps 266, 268 in thenoted mated sealed relation.

A third end cap 271, FIG. 17, is mounted to first pleated media filtersheet 206 of first panel 202 at second axial end 222 of wall segments210 of first pleated filter media sheet 206. A fourth end cap 272 ismounted to second pleated filter media sheet 228 of second panel 204 atfourth axial end 244 of wall segments 232 of second pleated filter mediasheet 228. Third and fourth end caps 271 and 272 are mated and sealed toeach other at 274 and span laterally along lateral direction 68 andtransversely along transverse direction 58. In the embodiment of FIG.17, the subassembly of mated end caps 271 and 272 form a closed end capcomparable to end cap 46 of FIG. 1. The subassembly of mated end caps266 and 268 form an end cap comparable to end cap 44 of FIG. 1, with anopening or port 276 therethrough communicating with the interior of thefilter element. Mated first and second end caps 266 and 268 are axiallydistally oppositely spaced from mated third and fourth end caps 270 and272 along axial direction 28. Mated end caps 266 and 268 have a centralinterface portion 278 with opening 276 extending axially therethroughproviding a port communicating the noted axial flow path segment 26therethrough, FIG. 1. Each of end caps 266 and 268 is an arcuate portionof a closed-loop annulus. Preferably end caps 266 and 268 are identical,for cost reduction. Likewise, end caps 270 and 272 are preferablyidentical. Further preferably, each of the noted end caps issemi-circular.

It is recognized that various equivalents, alternatives andmodifications are possible within the scope of the appended claims.

1. A filter for filtering fluid flowing along a flow path having firstand second segments, said first segment being a filtering path segment,said second segment being an axial flow path segment extending axiallyalong an axial direction along an axis, said first segment being normalto said second segment, said filter comprising an annular filter elementextending axially along said axis along said axial direction, saidfilter element comprising a pair of panels mating to form a closed-loopannulus, a first of said pair of panels comprising a first pleatedfilter media sheet having a plurality of pleats defined by wall segmentsextending along a transverse direction between first and second sets ofpleat tips at first and second sets of axially extending bend lines,said transverse direction being normal to said axis, said wall segmentsextending axially between first and second axial ends, said first panelspanning laterally along a lateral span along a lateral direction from afirst lateral end to a second lateral end, said lateral direction beingnormal to said transverse direction and normal to said axial direction,said wall segments having a pleat depth along said transverse directionbetween said first and second sets of pleat tips, said pleat depth ofsaid wall segments varying as said first panel spans laterally alongsaid lateral span from said first lateral end to said second lateralend, a second of said pair of panels comprising a second pleated filtermedia sheet having a plurality of pleats defined by wall segmentsextending along said transverse direction between third and fourth setsof pleat tips at third and fourth sets of axially extending bend lines,said wall segments of said second panel extending axially between thirdand fourth axial ends, said second panel spanning laterally along alateral span along said lateral direction from a third lateral end to afourth lateral end, said wall segments of said second panel having apleat depth along said transverse direction between said third andfourth sets of pleat tips, said pleat depth of said wall segments ofsaid second panel varying as said second panel spans laterally alongsaid lateral direction from said third lateral end to said fourthlateral end.
 2. The filter according to claim 1 wherein: said pleatdepth of said wall segments of said first panel varies as said firstpanel spans laterally along said lateral span from said first lateralend to said second lateral end such that said wall segments of saidfirst panel have a reduced pleat depth at said first lateral end thenincrease to an increased pleat depth at a central region between saidfirst and second lateral ends then decrease to a reduced pleat depth atsaid second lateral end; said pleat depth of said wall segments of saidsecond panel varies as said second panel spans laterally along saidlateral direction from said third lateral end to said fourth lateral endsuch that said wall segments of said second panel have a reduced pleatdepth at said third lateral end then increase to an increased pleatdepth at a central region between said third and fourth lateral endsthen decrease to a reduced pleat depth at said fourth lateral end. 3.The filter according to claim 2 wherein: said reduced pleat depth wallsegments at said first and second lateral ends of said first panel aredistally opposite each other along a first chord extending along saidlateral direction through said annular filter element; said reducedpleat depth wall segments at said third and fourth lateral ends of saidsecond panel are distally opposite each other along a second chordextending along said lateral direction through said annular filterelement.
 4. The filter according to claim 3 wherein said first andsecond chords are parallel to each other.
 5. The filter according toclaim 4 wherein: said first chord extends parallel to a projection lineextending laterally through the axial center line of said annular filterelement; said second chord extends parallel to said projection line andon the opposite transverse side thereof from said first chord.
 6. Thefilter according to claim 3 wherein said first and second chords arespaced by a transverse gap therebetween, and wherein said axial flowpath segment extends axially through said gap.
 7. The filter accordingto claim 6 wherein: said reduced pleat depth wall segments at said firstlateral end of said first panel are diametrically opposite said reducedpleat depth wall segments at said fourth lateral end of said secondpanel; said reduced pleat depth wall segments at said second lateral endof said first panel are diametrically opposite said reduced pleat depthwall segments at said third lateral end of said second panel.
 8. Thefilter according to claim 2 wherein said annular filter element iscylindrical.
 9. The filter according to claim 2 wherein: said first setof pleat tips lie along a first rectilinear projection line extendingalong said lateral direction; said third set of pleat tips lie along asecond rectilinear projection line extending along said lateraldirection and transversely spaced from said first rectilinear projectionline.
 10. The filter according to claim 1 comprising a first end capmounted to said first pleated filter media sheet of said first panel atsaid first axial end of said wall segments of said first pleated filtermedia sheet, a second end cap mounted to said second pleated filtermedia sheet of said second panel at said third axial end of said wallsegments of said second pleated filter media sheet, said first andsecond end caps being mated to each other and spanning laterally alongsaid lateral direction and transversely along said transverse direction.11. The filter according to claim 10 comprising a third end cap mountedto said first pleated filter media sheet of said first panel at saidsecond axial end of said wall segments of said first pleated filtermedia sheet, a fourth end cap mounted to said second pleated filtermedia sheet of said second panel at said fourth axial end of said wallsegments of said second pleated filter media sheet, said third andfourth end caps being mated to each other and spanning laterally alongsaid lateral direction and transversely along said transverse direction,said mated first and second end caps being axially distally oppositelyspaced from said mated third and fourth end caps along said axialdirection.
 12. The filter according to claim 10 wherein said mated firstand second end caps have a central interface portion with an openingextending axially therethrough providing a port communicating said axialflow path segment therethrough.
 13. The filter according to claim 10wherein each of said first and second end caps is an arcuate portion ofa closed-loop annulus.
 14. The filter according to claim 13 wherein saidfirst and second end caps are identical.
 15. The filter according toclaim 14 wherein each of said first and second end caps issemi-circular.